The crawler tractor has countless applications throughout the world in construction and related industries. It is often used as a bulldozer with the attachment of a bulldozer blade, or with a rear mounted ripper for trenching and the like.
Virtually all crawler tractor designs provide for some suspension or spring action and include portions which are included in the sprung weight of the machine, with other portions included in the unsprung weight. The sprung weight of the machine usually includes the tractor chassis, engine, power train, radiator and the blade mounting equipment. The unsprung weight usually includes the crawler tracks, the track frames, track rollers, front idlers and top idlers.
The sprung weight of the typical machine is supported at three points. An equalizer bar, which functions essentially as a single leaf spring, is pivoted at its center to the sprung weight of the machine and is supported at its ends to the left and right track frames, respectively, and forms the first point. The second and third points of support are the left and right track frame pivot shafts at the rear of the machine about which the track frames have limited pivotal motion.
The spring action of the equalizer bar to some extent isolates the front of the tractor from vibration and shock loads in the unsprung weight. However, traditionally the pivot shafts have been mounted through solid metal to metal contact with the track frames, providing an uninterrupted path for shock and vibration transfer to the machine operator and the tractor machinery.
Several attempts have been made in the past to improve upon the conventional crawler tractor suspension. For example, defensive publication T No. 982,002, published May 1, 1979, discloses a pivot shaft bushing including an elastomeric sleeve. U.S. Pat. No. 3,096,840, issued July 9, 1963, discloses a tractor suspension which employs an annular mass of resilient cushioning material in the suspension. U.K. Patent Reference No. 2,155,415A discloses a crawler vehicle which uses pad cushion rubbers. U.S. Pat. No. 3,826,325, issued July 30, 1974 discloses a track suspension assembly having stops formed of resilient rubber pads such as pads 100 and 102 to cushion movement of crank members 22 and 38. U.K. Patent Reference No. 2,124,563A discloses a sprocket wheel assembly of endless track-type vehicles. It incorporates elastic annular blocks 42 and 43 to mount outer tube 41 on the inner tubes 27 and 35 of a sprocket assembly to absorb shock. However, none of these designs have proven practical in the severe environments in which these crawler tractors must be employed. A need therefore exists for a practical suspension system which reduces the transfer of vibration and stress to the unsprung weight of the machine.